1. Field of Invention
This invention relates to the field of pictorial data recording.
2. Description of Prior Art
The problem solved by this invention is that of devising a means for recording essentially three- or four-dimensional data as a two-dimensional pictorial recording in true or false color.
An example of three-dimensional data which may be so recorded is earth survey data representing surface temperature at each point in a region of the earth's surface, the two spatial dimensions, together with the value assigned to each point providing the three-dimensional nature of the data. Other examples of three-dimensional data are the total intensity of light reflected from each point in a region, the magnetic field intensity at each point in a region, and the like.
An example of what is essentially a four-dimensional data matrix is the observed color of visible light reflected from each point in a region of the earth's surface. Here two dimensions of the data matrix are provided by the two spatial dimensions of the region being surveyed, the third (spectral) dimension is provided by the total spectral bandwidth of the sensor or other data acquisition means; and the fourth dimension is provided by the observed intensity of light within each of the incremental component bands of this spectrum. In effect, therefore, an ordinary color photograph is a recording of four-dimensional data of this sort.
The problem exists, however, in making a continuous two-dimensional true- or false-color hard-copy recording corresponding to three and, particularly, four-dimensional data as it is acquired (i.e., in real time) or from data which has previously been recorded by ordinary electronic means, such as a tape recorder.
We will assume, for discussion purposes, that in our four-dimensional example, data is acquired through a satellite sensor line scan of the earth's surface. Here, one of the dimensions is the direction of the satellite motion, which can be thought of as spatial (although it is really temporal). The second dimension is the spatial dimension transverse to that of the satellite motion, representing position along a particular scan line. The third dimension is the spectral range (e.g., visible light, gamma radiation, near-or far-infrared, etc.) of the sensor which is acquiring the optical data. Finally, the fourth dimension is the observed intensity within each incremental spectral band.
Ordinarily such data is recorded on a multi-channel tape recorder. The instantaneous amplitude of the signal in each channel represents either the instantaneous amplitude or intensity of the light observed within a corresponding spectral band.
Several means have heretofore been employed in producing true- or false-color recordings of this type of data.
One such means is to acquire or convert the spectral data into three channels of information corresponding, respectively, to the intensities of the red, blue and green components of the light. The entire data matrix (or a large spatial portion of it) is displayed as a single, two-dimensional image on a color TV screen and color photographed.
The problem with this method is that resolution is limited by the 525-line limit of the ordinary color TV screen. If more than 525 scan lines are included in the data matrix, a continuous photographic recording cannot be made, except by developing the final print as a series of 525-line frames placed end to end.
Another method is similar to the last, except that a black-and-white CRT is employed. As in the color TV case, data from a single one of the three channels is displayed on the screen. The image is passed through a filter whose color corresponds to the spectral band of the particular data channel, and the filtered image is photographed on color film. This is repeated for the other two channels. The resulting photograph consists of the three images superimposed. This method presents all the inherent difficulties of the aforementioned color TV method, and introduces, in addition, the problem of precise registration of the three superimposed images.
All such systems are also deficient in that they provide little flexibility in altering the scan rate, in the density of data produced on the final photograph, and in their false-color capability.